Arylpiperazine opioid receptor antagonists

ABSTRACT

Provided are opioid receptor antagonists represented by the formula (I) where R, Y 3 , R 1 , R 2 , R 3 , R 4  and R 5  are as defined herein.

RELATED APPLICATION INFORMATION

This application claims priority to U.S. provisional application Ser. Nos. 61/307,534, filed on Feb. 24, 2010 and 61/316,423, filed on Mar. 23, 2010, both incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to 4-arylpiperazine compounds. These compounds function as opioid receptor antagonists, and can be used to treat a variety of disease states.

2. Description of the Background

The opioid receptors, μ, δ, κ, and the opioid-like receptor ORL-1 belong to the super family of G-protein coupled receptors (GPCRs) that possess seven helical trans-membrane spanning domains in their architecture.¹ The majority of research efforts focused upon this group of proteins has been directed toward the μ receptor since it mediates the actions of both the opiate and opioid analgesics such as morphine and fentanyl, respectively.² However, over the years it has become increasingly clear that the entire family of proteins is actively involved in a host of biological processes.² Furthermore, the advent of selective antagonists has demonstrated that pharmacotherapeutic opportunities exist via both negative and positive modulation of this receptor family.³⁻⁸

The opioid receptor system has been extensively studied, and thousands of compounds have been synthesized and evaluated by in vitro binding and functional assays as well as by animal models.² An integral part of the effort to characterize the opioid receptor system has been the discovery of potent, pure antagonists. Naloxone (1a) and naltrexone (1b), both competitive antagonists at μ, δ, and κ opioid receptors,⁹ have been extensively used as pharmacological tools to identify and characterize opioid systems (see FIG. 1 for structures). Additionally, naloxone is approved to treat heroin overdose and to reverse respiratory depression caused by morphine.⁹ Naltrexone is used to treat heroin and alcohol abuse.

In 1978, Zimmerman and co-workers reported the discovery of a structurally unique series of opioid receptor pure antagonists based on N-substituted analogues of 3,4-dimethyl-4-(3-hydroxyphenyl)piperidine (2a, LY272922).¹⁰ Unlike naloxone (1a) and naltrexone (1b) where the antagonist activity is dependent on the N-allyl or N-cyclopropylmethyl substituent, all N-substituted trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidines (2) including the N-methyl analogue 2b are opioid receptor pure antagonists.¹⁰⁻¹⁴ A few of the more interesting analogues include alvimopan (3), which is an FDA-approved drug for GI motility disorder,¹⁵ LY255,582 (2d),^(13,16) which was developed to treat obesity, and the selective κ opioid receptor antagonist JDTic (4),^(6-8,17) which shows activity in rat models of depression,¹⁸ anxiety,¹⁹ and stress-induced cocaine relapse.¹⁸ JDTic appears to be a promising therapeutic.

Komoto et al. reported structures like 6a-f in a paper entitled “New μ-Opioid Receptor Agonists with piperazine Moiety.” They do not describe that the compounds have opioid receptor antagonistic efficacy.²⁰ The compounds are synthesized by a route similar to that used to prepare 5a-j. At present, the opiate class, represented by naloxone (1a), naltrexone (1b), and the N-substituted 3,4-dimethyl-4-(3-hydroxyphenyl)piperidines, represented by alvimopan, LY255,582, and JDTic, are the only two classes of nonpeptide pure opioid receptor antagonists known. The discovery that 3-[4-(substituted piperazine-yl)]phenols (5) as described herein are pure opioid receptor antagonists adds a third example of this important class of compounds.

Studies with selective κ opioid antagonists have shown that this system is intimately involved in brain processes that relate to stress, fear, and anxiety as well as reward-seeking behavior. Studies have shown that JDTic (4) and nor-BNI, another κ opioid selective antagonist, dose-dependently reduce fear and stress-induced responses in multiple behavioral paradigms with rodents (immobility in the forced-swim assay,^(18,21) reduction of exploratory behavior in the elevated plus maze, and fear-potentiated startle).¹⁹ Furthermore, selective κ antagonists have been shown to reduce stress-induced reinstatement of cocaine self-administration in rats,¹⁸ to block the stress-induced potentiation of cocaine place preference conditioning,²²⁻²⁴ to decrease dependence-induced ethanol self-administration,²⁵ to diminish deprivation-induced eating in rats,²⁶ and to prevent pre-pulse inhibition mediated by U50,488.²⁷ These observations regarding the behavioral consequences of receptor blockade in several animal tests suggest that κ antagonists will be useful for treating anxiety, depression, schizophrenia, addiction, and eating disorders.

Previously reported non-selective opioid receptor antagonists such as LY255582 have been found to increase metabolic energy consumption and reduce the weight in obese rats while maintaining muscle mass. These reports suggest that opioid receptor antagonists may be useful in preventing, treating, and/or ameliorating the effect of obesity. Eli Lilly and Company has developed new classes of opioid receptor antagonists that interact with the μ, δ, and κ receptors (termed non-selective) as potential pharmacotherapies to treat obesity and related diseases.^(28,29) The Lilly patents suggest that such compounds will be useful for the treatment and/or prophylaxis of obesity and related diseases including eating disorders (bulimia, anorexia nervosa, etc.), diabetes, diabetic complications, diabetic retinopathy, sexual/reproductive disorders, depression, anxiety, epileptic seizure, hypertension, cerebral hemorrhage, congestive heart failure, sleeping disorders, atherosclerosis, rheumatoid arthritis, stroke, hyperlipidemia, hypertriglycemia, hyperglycemia, hyperlipoproteinemia, substance abuse, drug overdose, compulsive behavior disorders (such as paw licking in dog), and addictive behaviors such as for example gambling and alcoholism.

SUMMARY OF THE INVENTION

Aryl-substituted piperazines (5) are a new class of opioid receptor antagonists (see the Examples section below for representative structures). Similar to the N-substituted 3,4-dimethyl-4-(3-hydroxyphenyl)piperidines, even the N-methyl substituted analog 5f is a pure opioid antagonist. Changing the N-substituent to an N-phenylpropyl group gives 5b, which has K_(e) values of 0.88, 13.4, and 4.09 nM at μ, δ, and κ opioid receptors, which are similar to the K_(e) values of N-phenylpropyl 3,4-dimethyl-4-(3-hydroxyphenyl)piperidine 2c (RTI-5989-264). The JDTic-like analog from this class 5j has K_(e) values of 22, 274, and 2.7 nM at the μ, δ, and κ opioid receptors, respectively (see Table 1). All compounds of this class thus far synthesized are relatively nonselective opioid receptor antagonists. Thus, their opioid receptor properties are more like those of naloxone (1a), naltrexone (1b), and the originally reported N-substituted 3,4-dimethyl-4-(3-hydroxyphenyl)piperidines.¹³

Thus, the present invention is directed to aryl-substituted piperazine opioid receptor antagonists represented by the formula (I):

wherein

R is hydrogen, OH, OC₁₋₆ alkyl, C₁₋₈ alkyl, C₁₋₈ haloalkyl, C₂₋₈ alkenyl, C₂₋₈ alkynyl, aryl substituted by one or more groups Y₁, CH₂-aryl wherein the aryl group is substituted by one or more groups Y₁, OCOC₁₋₈ alkyl, COC₁₋₈ alkyl, CONH₂, NHCHO, NH₂, NHSO₂C₁₋₈ alkyl, or NHCO₂C₁₋₈ alkyl;

Y₃ is hydrogen, Br, Cl, F, CN, CF₃, NO₂, OR₈, CO₂R₉, C₁₋₆ alkyl, NR₁₀R₁₁, NHCOR₁₂, NHCO₂R₁₂, CONR₁₃R₁₄ or CH₂(CH₂)_(n)Y₂;

R₁, R₂, R₃ and R₄ are each, independently, one of the following structures:

or R₁ and R₂, R₂ and R₃ and/or R₃ and R₄ are bonded together to form a cyclo alkyl group or a bridged heterocyclic ring;

each Y₁ is, independently, hydrogen, OH, Br, Cl, F, CN, CF₃, NO₂, N₃, OR₈, CO₂R₉, C₁₋₆ alkyl, NR₁₀R₁₁, NHCOR₁₂, NHCO₂R₁₂, CONR₁₃R₁₄, or CH₂(CH₂)_(n)Y₂, or two adjacent Y₁ groups form a —O—CH₂—O— or —O—CH₂CH₂—O— group;

each Y₂ is, independently, hydrogen, CF₃, CO₂R₉, C₁₋₈ alkyl, NR₁₀R₁₁, NHCOR₁₂, NHCO₂R₁₂, CONR₁₃R₁₄, CH₂OH, CH₂OR₈, COCH₂R₉,

each n is, independently, 0, 1, 2 or 3;

each o is, independently, 0, 1, 2 or 3;

each R₈, R₉, R₁₀, R₁₁, R₁₂, R₁₃ and R₁₄ is, independently, hydrogen, C₁₋₈ alkyl, CH₂-aryl wherein the aryl group is substituted by one or more substituents OH, Br, Cl, F, CN, CF₃, NO₂, N₃, C₁₋₆ alkyl, or CH₂(CH₂)_(n)Y₂′;

each Y₂′ is, independently, hydrogen, CF₃, or C₁₋₆ alkyl;

R₅ is

—CH₂CH₂—X—R₆, or

R₆ is C₁₋₈ alkyl, C₂₋₈ alkenyl, C₁₋₄ alkyl substituted C₄₋₈ cycloalkyl, C₁₋₄ alkyl substituted C₄₋₈ cycloalkenyl, or thiophene;

X is a single bond, —C(O)— or —CH(OR₁₅)—;

R₁₅ hydrogen, C₁₋₆ alkyl, —(CH₂)_(q)-phenyl or —C(O)—R₁₆;

R₁₆ is C₁₋₄ alkyl or —(CH₂)_(q)-phenyl;

each q is, independently, 1, 2 or 3;

R₁₇ is hydrogen, C₁₋₈ alkyl, CO₂C₁₋₈ alkylaryl substituted by one or more groups Y₁, CH₂-aryl substituted by one or more groups Y₁, or CO₂C₁₋₈ alkyl;

R₁₈ is hydrogen, C₁₋₈ alkyl, C₂₋₈ alkenyl, C₃₋₈ alkynyl, CH₂CO₂C₁₋₈ alkyl, CO₂C₁₋₈ alkyl or CH₂-aryl substituted by one or more groups Y₁;

R₁₉ is a group selected from the group consisting of structures (a)-(p):

Q is NR₂₁, CH₂, O, S, SO, or SO₂;

each Y₄ is, independently, Br, Cl, F, CN, CF₃, NO₂, N₃, OR₂₂, CO₂R₂₃, C₁₋₆ alkyl, NR₂₄R₂₅, NHCOR₂₆, NHCO₂R₂₇, CONR₂₈R₂₉, or CH₂(CH₂)_(n)Y₂,

or two adjacent Y₄ groups form a —O—CH₂—O— or —O—CH₂CH₂—O— group;

p is 0, 1, 2, or 3;

R₂₀ is hydrogen, C₁₋₈ alkyl, C₂₋₈ alkenyl, C₂₋₈ alkenyl, CH₂OR₃₀, or CH₂-aryl substituted by one or more substituents Y₁;

each R₂₁ is, independently, hydrogen, C₁₋₈ alkyl, CH₂-aryl substituted by one or more substituents Y₁, NR₃₁R₃₂, NHCOR₃₃, NHCO₂R₃₄, CONR₃₅R₃₆, CH₂(CH₂)_(n)Y₂, or C(═NH)NR₃₇R₃₈,

R₃₀ is hydrogen C₁₋₈ alkyl, C₂₋₈ alkenyl, C₂₋₈ alkenyl, CH₂O₂C₁₋₈ alkyl, CO₂C₁₋₈ alkyl, or CH₂-aryl substituted by one or more substituents Y₁;

R₂₂, R₂₃, R₂₄, R₂₅, R₂₆, R₂₇, R₂₈, R₂₉, R₃₁, R₃₂, R₃₃, R₃₄, R₃₅, R₃₆, R₃₇ and R₃₈ are, independently, hydrogen, C₁₋₈ alkyl, CH₂-aryl substituted by one or more substituents OH, Br, Cl, F, CN, CF₃, NO₂, N₃, C₁₋₆ alkyl, or CH₂(CH₂)_(n)Y₂′;

Z is N, O or S, wherein when Z is O or S, there is no R₁₈;

X₁ is hydrogen, C₁₋₈ alkyl, C₂₋₈ alkenyl, or C₂₋₈ alkynyl;

X₂ is hydrogen, C₁₋₈ alkyl, C₂₋₈ alkenyl, or C₂₋₈ alkynyl;

or X₁ and X₂ together form ═O, ═S, or ═NH,

with the proviso that when R₅ is;

then at least one of R₁, R₂, R₃ and R₄ is other than hydrogen as defined above;

or a pharmaceutically acceptable salt thereof.

The present invention also includes pharmaceutical compositions, which comprise the opioid receptor antagonist described above and a pharmaceutically acceptable carrier.

The present invention also includes a method of antagonizing opioid receptors, comprising administering an effective amount of the opioid receptor antagonist discussed above to a subject in need thereof.

The present invention also includes a method of treating drug addiction, drug abuse, depression, anxiety, schizophrenia, obesity and eating disorders, comprising administering an effective amount of the opioid receptor antagonist discussed above to a subject in need thereof.

The present invention also includes a method of treating alcohol addiction, nicotine addiction, cocaine addition and methamphetamine addiction, comprising administering an effective amount of the opioid receptor antagonist discussed above to a subject in need thereof.

The present invention also includes a method of treating diabetes, diabetic complications, diabetic retinopathy, sexual/reproductive disorders, epileptic seizure, hypertension, cerebral hemorrhage, congestive heart failure, sleeping disorders, atherosclerosis, rheumatoid arthritis, stroke, hyperlipidemia, hypertriglycemia, hyperglycemia, hyperlipoproteinemia, substance abuse, drug overdose, compulsive behavior disorders and addictive behaviors, comprising administering an effective amount of the opioid receptor antagonist discussed above to a subject in need thereof.

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following Figures in conjunction with the detailed description below.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1: chemical structure of compounds 1-6.

DETAILED DESCRIPTION OF THE INVENTION

A broad description of the invention is provided in the Summary section above.

In another embodiment of the invention:

R is hydrogen, OH, OC₁₋₃ alkyl, C₁₋₄ alkyl, C₁₋₄ haloalkyl, C₂₋₄ alkenyl, C₂₋₄ alkynyl, aryl substituted by one or more groups Y₁, CH₂-aryl wherein the aryl group is substituted by one or more groups Y₁, OCOC₁₋₄ alkyl, COC₁₋₄ alkyl, CONH₂, NHCHO, NH₂, NHSO₂C₁₋₄ alkyl, or NHCO₂C₁₋₄ alkyl; and

Y₃ is hydrogen, Br, Cl, F, CN, CF₃, NO₂, OR₈, CO₂R₉, C₁₋₃ alkyl, NR₁₀R₁₁, NHCOR₁₂, NHCO₂R₁₂, CONR₁₃R₁₄ or CH₂(CH₂)_(n)Y₂;

In another embodiment of the invention, R₁, R₂, R₃ and R₄ are each, independently, one of the following structures:

or R₁ and R₂, R₂ and R₃ and/or R₃ and R₄ are bonded together to 5 to 7 membered alkyl group or a bridged heterocyclic ring.

In another embodiment of the invention, R₅ is

or

In another embodiment of the invention, at least one of R₁, R₂, R₃ and R₄ is other than hydrogen.

In another embodiment of the invention, R is hydrogen, OH, OC₁₋₂ alkyl, C₁₋₂ alkyl, C₁₋₂ haloalkyl, C₂₋₃ alkenyl, C₂₋₃ alkynyl, aryl substituted by one or more groups Y₁, CH₂-aryl wherein the aryl group is substituted by one or more groups Y₁, COC₁₋₂ alkyl, CONH₂, NHCHO, NH₂, NHSO₂C₁₋₂ alkyl, or NHCO₂C₁₋₂ alkyl.

In another embodiment of the invention, R is hydrogen, OH, OCH₃, OCF₃, COCH₃, OCOCH₃, CONH₂, NHCHO, NH₂, NHSO₂CH₃, or NHCO₂CH₃.

In another embodiment of the invention, R is hydrogen, OH, OCH₃, or OCF₃.

In another embodiment of the invention, Y₃ is hydrogen.

In another embodiment of the invention, R₁, R₂, R₃ and R₄ are each, independently, one of the following structures:

or R₁ and R₂, R₂ and R₃ and/or R₃ and R₄ are bonded together to 5 to 7 membered alkyl group or a bridged heterocyclic ring.

In another embodiment of the invention, R₁, R₂, R₃ and R₄ are each, independently, hydrogen, methyl or ethyl.

In another embodiment of the invention, R₁, R₂, R₃ and R₄ are each, independently, hydrogen or methyl.

In another embodiment of the invention, R₁, R₂, R₃ and R₄ are each, independently, hydrogen or methyl, wherein at least one of R₁, R₂, R₃ and R₄ is methyl.

In another embodiment of the invention, R₅ is hydrogen, C₁₋₄ alkyl or —(CH₂)_(n)-phenyl.

In another embodiment of the invention, R₅ is

In another embodiment of the invention:

R is hydrogen, OH, OCH₃, or OCF₃;

Y₃ is hydrogen;

R₁, R₂, R₃ and R₄ are each, independently, hydrogen, methyl or ethyl; and

R₅ is hydrogen, C₁₋₄ alkyl or —(CH₂)_(n)-phenyl.

In one preferred embodiment, R₂ is other than hydrogen as defined above. This substitution may increase opioid efficacy by an order of magnitude. The chiralty at the resulting stereocenter may be (R) or (S). Preferred substituents are C₁₋₈ alkyl, preferably methyl, ethyl and propyl.

In another embodiment of the invention at least one of R₁, R₂, R₃ and R₄ is other than hydrogen as defined above when R₅ is

In another preferred embodiment of the present invention, the opioid receptor antagonists are as described in the following Examples section.

The present invention includes any and all combination of the different structural groups defined above, including those combinations not specifically set forth above.

As used throughout this disclosure, the terms “alkyl group” or “alkyl radical” encompass all structural isomers thereof, such as linear, branched and cyclic alkyl groups and moieties. Unless stated otherwise, all alkyl groups described herein may have 1 to 8 carbon atoms, inclusive of all specific values and subranges therebetween, such as 2, 3, 4, 5, 6, or 7 carbon atoms. Representative examples include methyl, ethyl, propyl and cyclohexyl.

As used throughout this disclosure, the terms “haloalkyl group” or “haloalkyl radical” encompass all structural isomers thereof, such as linear, branched and cyclic groups and moieties. Unless stated otherwise, all haloalkyl groups described herein may have 1 to 8 carbon atoms, inclusive of all specific values and subranges therebetween, such as 2, 3, 4, 5, 6, or 7 carbon atoms. A C₁₋₂ haloalkyl group is particularly preferred. At least one hydrogen atom is replaced by a halogen atom, i.e., fluorine, chlorine, bromine or iodine. In one embodiment, all of the hydrogen atoms are replaced with halogen atoms. Fluorine is preferred. Perfluoroalkyl groups are particularly preferred. Examples of haloalkyl groups include trifluoromethyl (—CF₃) and perfluoroethyl (—CF₂CF₃).

The alkenyl group or alkynyl group may have one or more double or triple bonds, respectively. As will be readily appreciated, when an alkenyl or alkynyl group is bonded to a heteroatom a double or triple bond is not formed with the carbon atom bonded directly to the heteroatom. Unless stated otherwise, all alkenyl and alkynyl groups described herein may have 2 to 8 carbon atoms, inclusive of all specific values and subranges therebetween, such as 3, 4, 5, 6, or 7 carbon atoms. Preferred examples include —CH═CH₂, —CH₂CH═CH₂, —CCH and —CH₂CCH.

The aryl group is a hydrocarbon aryl group, such as a phenyl, naphthyl, phenanthryl, anthracenyl group, which may have one or more C₁₋₄ alkyl group substituents.

The compounds of the present invention may be in the form of a pharmaceutically acceptable salt via protonation of the amines with a suitable acid. The acid may be an inorganic acid or an organic acid. Suitable acids include, for example, hydrochloric, hydroiodic, hydrobromic, sulfuric, phosphoric, citric, acetic, fumaric, tartaric, and formic acids.

The opioid receptor selectivity may be determined based on the binding affinities at the receptors indicated or their selectivity in opioid functional assays.

The compounds of the present invention may be used to bind opioid receptors. Such binding may be accomplished by contacting the receptor with an effective amount of the inventive compound. Of course, such contacting is preferably conducted in an aqueous medium, preferably at physiologically relevant ionic strength, pH, etc. Receptor antagonism is the preferred mode of action of the compounds described herein.

The inventive compounds may also be used to treat patients having disease states which are ameliorated by binding opioid receptors or in any treatment wherein temporary suppression of the kappa opioid receptor system is desired. Such diseases states include opiate addiction (such as heroin addiction), cocaine, nicotine, or ethanol addiction. The compounds of the present invention may also be used as cytostatic agents, as antimigraine agents, as immunomodulators, as immunosuppressives, as antiarthritic agents, as antiallergic agents, as virucides, to treat diarrhea, as antipsychotics, as antischizophrenics, as antidepressants, as uropathic agents, as antitussives, as antiaddictive agents, as anti-smoking agents, to treat alcoholism, as hypotensive agents, to treat and/or prevent paralysis resulting from traumatic ischemia, general neuroprotection against ischemic trauma, as adjuncts to nerve growth factor treatment of hyperalgesia and nerve grafts, as anti-diuretics, as stimulants, as anti-convulsants, or to treat obesity. Additionally, the present compounds can be used in the treatment of Parkinson's disease as an adjunct to L-dopa for treatment of dyskinesia associated with the L-dopa treatment.

The compounds of the present invention are particularly useful for treating addiction, such as addiction to cocaine, alcohol, methamphetamine, nicotine, heroine, and other drugs of abuse. With respect to nicotine, the compounds of the present invention are also useful in treating nicotine withdrawal effects.

The compounds may be administered in an effective amount by any of the conventional techniques well-established in the medical field. For example, the compounds may be administered orally, intraveneously, or intramuscularly. When so administered, the inventive compounds may be combined with any of the well-known pharmaceutical carriers and additives that are customarily used in such pharmaceutical compositions. For a discussion of dosing forms, carriers, additives, pharmacodynamics, etc., see Kirk-Othmer Encyclopedia of Chemical Technology, Fourth Edition, Vol. 18, 1996, pp. 480-590, incorporated herein by reference. The patient is preferably a mammal, with human patients especially preferred. Effective amounts are readily determined by those of ordinary skill in the art. Studies by the present inventors show no toxicity and no lethality for the present compounds at amounts up to 300 mg/kg in mice.

The compounds of the present invention can be administered as a single dosage per day, or as multiple dosages per day. When administered as multiple dosages, the dosages can be equal doses or doses of varying amount, based upon the time between the doses (i.e. when there will be a longer time between doses, such as overnight while sleeping, the dose administered will be higher to allow the compound to be present in the bloodstream of the patient for the longer period of time at effective levels). Preferably, the compound and compositions containing the compound are administered as a single dose or from 2-4 equal doses per day.

Suitable compositions containing the present compounds further comprise a physiologically acceptable carrier, such as water or conventional pharmaceutical solid carriers, and if desired, one or more buffers and other excipients.

The compounds of the invention may be synthesized by, for example, the schemes shown in the following Examples. Those skilled in the art will appreciate that the synthesis of the exemplified compounds can readily be adapted for the preparation of other compounds within the scope of formula I.

EXAMPLES

Having generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified.

Chemistry and Biology

Compounds 5a-f of the present invention may be synthesized, for example, in accordance with the reaction sequence shown in Scheme 1. The tert-butoxycarbonyl-protected starting piperazines 7a-e were prepared by treating the appropriate piperazine with Boc₂O or Boc-ON using standard conditions. The piperazines required for 7a-d were commercially available. Piperazine needed for 7e was synthesized according to reported methods.^(1,2) The tert-butoxycarbonyl-protected piperazines 7a-e were coupled to 3-bromoanisole under palladium-catalyzed conditions to give 8a-e. Treatment of 8a-e with boron tribromide in methylene chloride at −78° C. effected removal of the tert-butoxycarbonyl group and demethylation of the methyl ether to give 9a-e. Reductive alkylation of 9a-e using 3-phenylpropionaldehyde and sodium triacetoxyborohydride in 1,2-dichloroethane yielded the desired 5a-e. Reductive alkylation of 9b using formaldehyde and Raney nickel under a hydrogen atmosphere yielded 5f.

Compounds 5g,h can be synthesized by the routes shown in Scheme 2. Compound 10 was coupled to 3-bromoanisole under palladium-catalyzed conditions to give 11. Subjection of 11 to palladium on carbon in refluxing aqueous acetic acid removed the N-allyl-protecting group to give 12. Treatment of 12 with boron tribromide in methylene chloride at −78° C. affected demethylation of 12 to give the phenol 13. Reductive alkylation of 13 using 3-phenylpropionaldehyde and sodium triacetoxyborohydride in 1,2-dichloroethane yielded 6h. Treatment of 10 with (Boc₂)O in methylene chloride containing triethylamine gives the N-allyl, N-Boc-protected piperazine 14. Subjection of 14 to palladium on carbon in refluxing aqueous acetic acid selectively removed the N-allyl group to give 15. Compound 15 was coupled to 3-bromoanisole under palladium-catalyzed conditions to yield 16. Treatment of 16 with boron tribromide in methylene chloride at −78° C. effected removal of the tert-butoxycarbonyl group and demethylation of the methyl ether to give 17. Reductive alkylation of 17 using 3-phenylpropanaldehyde and sodium triacetoxyborohydride in 1,2-dichloroethane afforded the desired 5g.

Scheme 3 outlines the synthesis of 5i and 5j. Compound 9b is coupled with N-Boc-valine using BOP to give an amide which is not isolated but reduced directly to 5i using diborane in tetrahydrofuran. Coupling of 5i with 7-OH-Boc-D-Tic using BOP in tetrahydrofuran followed by treatment with trifluoroacetic acid in methylene chloride yielded 5j.

Biology

Measures of opioid receptor antagonism and specificity were obtained by monitoring the ability of selected test compounds to inhibit stimulation of [³⁵S]GTPγS binding produced by the selective agonists (D-Ala²,MePhe⁴,Gly-ol⁵)enkephalin (DAMGO, mu receptor) cyclo[D-Pen²,D-Pen⁵]enkephalin (DPDPE, delta) and 5,7,8-(−)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro[4,5]dec-8-yl]benzeneacetamide (U69,593, kappa) in cloned human receptors (Table 1).

Results

Compounds 5a-j show high efficacy (low K_(e) values) for the kappa opioid receptor in the [³⁵S]GTPγS in vivo functional assay, particularly 5b-e, 5g, and 5j. The compounds of the present invention are potent kappa opioid receptor antagonists in an in vitro functional test. Some compounds showed good selectivity for the kappa relative to the mu and delta opioid receptors.

Experimental General Procedures for the Preparation of 3-[4-(Substituted piperazin-1-yl)]phenols (6a-e)

a. Palladium-Catalyzed 3-Methoxyphenylation Procedure.

In a thick-walled glass sealable tube, 1 eq of piperazine 7a-c was dissolved in 20 mL of dry toluene along with 1.5 eq of 3-bromoanisole, 0.005 eq of Pd₂(dba)₃, 1.5 eq of KOtBu, and 0.01 eq of P(tBu)₃ as a 1M solution in toluene. The tube was flushed with argon, sealed, and heated to 110° C. for 16 h. The vessel was cooled to room temperature, opened, and the contents filtered through celite. The filtered solution was reduced to a fifth of its volume by evaporation under reduced pressure. The remaining solution was subjected to column chromatography on silica gel eluting with hexanes-EtOAc (5:1). The combined fractions containing the product were subjected to rotary evaporation, and the remaining oil was dried under high vacuum.

b. Transition Metal-Free 3-Methoxyphenylation.³

In a round-bottom flask equipped with a condenser under an argon dry atmosphere, 1.1 eq of KN(Si(CH₃)₃)₂ was suspended in 7 mL of dry 1,4-dioxane. The piperazines 7d,e, 1 eq, was added followed by 1 eq of 3-bromoanisole. The reaction mixture was stirred at 100° C. for 2.5 h, cooled to room temperature, and quenched with H₂O (10 mL). To the mixture was added Et₂O (15 mL) and shaken vigorously. The layers were separated, and the aqueous layer was extracted twice with Et₂O (10 mL). The pooled organic solution was concentrated by rotary evaporation, and the residue was subjected to column chromatography on silica gel eluting with hexane-EtOAc (5:1). The combined fractions containing the product were subjected to rotary evaporation, and the remaining oil was dried under high vacuum.

c. Removal of the N-Boc and O-Me Protecting Groups with BBr₃.

Under an argon atmosphere, 1 eq of Boc-protected phenylpiperazine 8 was dissolved in CH₂Cl₂ (20 mL), and the solution was cooled to −78° C. Into this mixture, 4 eq of BBr₃ as a 1 M solution in CH₂Cl₂ were introduced. The reaction mixture was stirred for 4 h, warmed to 0° C., and stirred for an additional 2 h. Into this solution dry MeOH (20 mL) was slowly added, and the solution was stirred for 5 min. The solvents were then removed under reduced pressure at 25° C. The residue was redissolved in MeOH (20 mL), and the solvents were removed again under reduced pressure to afford a residue that was recrystallized or converted to the freebase and purified by column chromatography on silica gel to yield the product.

d. Removal of the N-Boc and O-Me Protecting Groups with Conc. HBr.

In a round-bottom flask 8 were dissolved in conc. HBr, and the solution was refluxed for 16 h. Removal of the solvents by rotary evaporation gave a residue that was dissolved in MeOH. This solution was stirred over excess NaHCO₃ for 10 min and then filtered. The solution was concentrated under reduced pressure and subjected to column chromatography on silica gel to afford the product.

e. Reductive Alkylation of 9a-e with 3-Phenylpropanaldehyde.

In a dry flask 1 eq of phenylpiperazine 9a-e was dissolved in 1,2-dichloroethane (20 mL) along with 1.5 eq of 3-phenylpropanaldehyde and 1.5 eq of Et₃N. The solution was cooled to 0° C., and 1.5 eq of Na(OAc)₃BH was then added. The reaction mixture was stirred for 1 h at 0° C., allowed to warm to 25° C. After stirring for 2 h, the reaction mixture was added to a concentrated solution of NaHCO₃ (20 mL) and shaken vigorously. The layers were separated, and the organic layer was washed once with H₂O (5 mL) and once with brine (5 mL). The organic solution was dried (MgSO₄), filtered, and the solvents removed under reduced pressure to yield the product which was purified as specified.

1-tort-Butoxycarbonyl-4-(3-methoxyphenyl)piperazine (8a)

General procedure a. was employed using 0.996 g (5.35 mmol) of commercially available Boc-piperazine 7a to obtain, after chromatography, 1.53 g (98%) of 8a as a yellowish solid: mp 62-63° C. ¹H NMR (CDCl₃) δ 7.18 (t, 1H), 6.54 (m, 1H), 6.46. (s, 1H), 6.45 (m, 1H), 3.79 (s, 3H), 3.57 (m, 4H), 3.13 (m, 4H), 1.48 (s, 9H). ESIMS: m/z 293 (M+H⁺, 100).

(S)-tert-Butyl-4-(3-methoxyphenyl)-3-methylpiperazine-1-carboxylate (8b)

General procedure a. was employed using 1.32 g (6.60 mmol) of Boc-piperazine 7b⁴ to obtain, after chromatography, 1.19 g (59%) of 8b as a yellow oil with spectra identical to that of 8c.

(R)-tert-Butyl-4-(3-methoxyphenyl)-3-methylpiperazine-1-carboxylate (8c)

General procedure a. was employed using 1.00 g (5.00 mmol) of Boc-piperazine 7b⁴ to obtain, after chromatography, 841 mg (55%) of 8c as a yellow oil. ¹H NMR (CDCl₃) δ 7.17 (t, 1H), 6.67 (d, 1H), 6.43. (d, 1H), 4.37 (bm, 1H), 3.84, (m, 1H), 3.79 (s, 3H), 3.77 (bd, 1H), 3.33 (m, 1H), 3.18 (bm, 2H), 1.48 (s, 9H), 1.01 (d, 3H). ESIMS: m/z 425 (M+Na⁺, 100).

(Z)-1-tert-Butoxycarbonyl-4-(3-methoxyphenyl)-3,5-dimethylpiperazine (8d)

General procedure b. was employed using 588 mg (2.74 mmol) of Boc-piperazine 7d to obtain, after chromatography, 407 mg (46%) of 8d as a yellow oil. ¹H NMR (CDCl₃) δ 7.20 (t, 1H), 6.69 (m, 3H), 4.15 (m, 0.7H), 3.89 (bm, 1.3H), 3.79 (s, 3H), 3.06 (m, 2H), 2.88 (m, 2H), 1.48 (d, 9H), 1.20 (d, 2.1H), 0.81 (d, 3.1H). ESIMS: m/z 321 (M+H⁺, 50).

(2S,5S)-1-tert-Butoxycarbonyl-4-(3-methoxyphenyl)-2,5-dimethylpiperazine (8e)

General procedure b. was employed using 433 mg (2.02 mmol) of Boc-piperazine 7e to obtain, after chromatography, 397 mg (65%) of 8e as a yellow oil. ¹H NMR (CDCl₃) δ 7.17 (t, 1H), 6.52 (d, 1H), 6.47-6.45 (m, 1H), 4.15 (q, 1H), 4.03-3.98 (m, 1H), 3.41 (q, 1H), 3.30 (dd, 1H), 2.97-2.90 (dd, 1H), 2.84 (dd, 1H), 1.45 (s, 9H), 1.32 (d, 3H), 1.04 (d, 3H). ESIMS: m/z 321 (M+H⁺, 50).

(2S,5R)-1-tert-Butoxycarbonyl-4-(3-methoxyphenyl)-2,5-dimethylpiperazine (16)

General procedure a. was employed using 1.04 g (3.79 mmol) of Boc-piperazine 15 to obtain, after chromatography, 288 mg (24%) of 16 as a yellow oil. ¹H NMR (CDCl₃) δ 7.12 (t, 1H), 6.46 (d, 1H), 6.37 (s, 1H), 6.35 (d, 1H), 4.39 (b, 1H), 3.94 (bm, 1H), 3.79 (s, 3H), 3.78 (m, 1H), 3.40 (dd, 1H), 3.25 (dd, 1H), 3.11 (d, 1H), 1.48 (s, 9H), 1.25 (d, 3H), 1.03 (d, 3H). ESIMS: m/z 221 (M-Boc+H⁺, 95;), 321 (M+H⁺, 20).

(2R,5S)-1-Allyl-4-(3-methoxyphenyl)-2,5-dimethylpiperazine (11)

General procedure a. was employed using 1.00 g (6.48 mmol) of allyl-piperazine 10⁵ to obtain, after chromatography, 715 mg (55% yield) of 11 as a yellow oil. ¹H NMR (CDCl₃) δ 7.19 (t, 1H), 6.67 (dd, 1H), 6.62 (m, 1H), 6.56 (dd, 1H), 5.91 (m, 1H), 5.27-5.17 (m, 2H), 3.79 (s, 3H), 3.45-3.26 (m, 2H), 3.13 (dd, 1H), 3.00-2.89 (m, 2H), 2.82-2.64 (m, 2H), 2.21 (dd, 1H), 1.06 (d, 3H), 0.98 (d, 3H). ESIMS: m/z 261 (M+H⁺, 100).

3-piperazine-phenol Dihydrobromide (9a)

General procedure d. was employed using 1.39 of 8a and 20 mL of conc. HBr. Recrystallization from MeOH gave 1.05 (65%) of 9a as pink crystals: mp>220° C. ¹H NMR (d₆-DMSO) δ 8.75 (bs, 2H), 7.29 (bs, 2H), 7.16 (t, 1H), 6.55 (d, 1H), 6.51 (s, 1H), 5.45 (d, 1H), 3.36 (m, 2H), 3.22 (m, 4H), 2.50 (m, 2H). ESIMS: m/z 179 (M+H⁺, 100).

(S)-3-(2-Methylpiperazin-1-yl)phenol (9b) Dihydrobromide

General procedure c. was employed using 714 mg (2.44 mmol) of 8b affording a tan solid that was triturated under cold MeOH and collected by filtration, 624 mg (76%): mp>220° C. This compound had identical spectral information as 9c (see below).

(R)-3-(2-Methylpiperazin-1-yl)phenol (9c) Dihydrobromide

General procedure c. was employed using 780 mg (2.54 mmol) of 8c affording a tan solid that was triturated under cold MeOH and collected by filtration, 685 mg (76%): mp>220° C. ¹H NMR (CD₃OD) δ 7.33 (q, 1H, ArH), 6.97 (d, 1H, ArH), 6.94 (s, 1H, ArH), 6.80 (d, 1H, ArH), 4.15 (m, 1H, NCH), 3.76 (m, 1H, NCH), 3.71 (bd, 2H, NCH), 3.49 (dd, 1H, NCH), 1.18 (d, 3H, CH₃). ESIMS: m/z 193 (M+H⁺, 100).

(Z)-3-(2,6-Dimethylpiperazin-1-yl)phenol (9d)

General procedure d. was employed using 407 mg (1.27 mmol) of 8d and 10 mL of conc. HBr. The dihydrobromide salt was dissolved in MeOH, stirred over 200 mg of NaHCO₃ for 10 min, and filtered. The solution was concentrated under reduced pressure and subjected to column chromatography on silica gel eluting with CMA80 to afford 180 mg (65%) of 9d as a brown solid: mp>220° C. ¹H NMR (CDCl₃) δ 7.15 (t, 1H), 6.68 (m, 2H), 3.14 (m, 4H), 2.71 (dd, 2H, J=12 Hz), 0.80 (d, 3H). ESIMS: m/z 207 (M+H⁺, 100).

(2S,5S)-3-(2,5-Dimethylpiperazin-1-yl)phenol (9e)

General procedure d. was employed using 397 mg (1.80 mmol) of 8e and 10 mL of conc. HBr. The dihydrobromide salt was dissolved in MeOH, stirred over 200 mg of NaHCO₃ for 10 min and then filtered. The solution was concentrated under reduced pressure and subjected to silica-gel column chromatography eluting with CMA80-CH₂Cl₂ (1:1) to afford 522 mg (29%) of 9e as a grey solid: mp>220° C. ¹H NMR (CDCl₃) δ 7.10 (q, 1H), 6.52 (m, 1H), 6.45 (s, 1H), 6.41 (m, 1H), 4.23 (m, 2H), 3.89-3.39 (m, 4H), 3.03 (dd, 2H), 1.45 (d, 3H), 1.15 (d, 3H). ESIMS: m/z 207 (M+H⁺, 100).

3-[(2S,5R)-2,5-Dimethylpiperazin-1-yl]phenol (17) Dihydrobromide

General procedure c. was employed using 288 mg (0.90 mmol) of 16 affording a crimson-colored residue that was pure by NMR (100%). ¹H NMR (CD₃OD) δ 7.44 (t, 1H), 7.23 (m, 2H), 6.97 (m, 1H), 4.39 (m, 1H), 4.22 (m, 1H), 3.97-3.82 (m, 2H), 3.71 (m, 1H), 3.29 (m, 1H), 1.48 (d, 3H), 1.25 (d, 3H). ESIMS: m/z 207 (M+H⁺, 100).

3-[(2R,5S)-2,5-Dimethylpiperazin-1-yl]phenol (13)

In a round-bottom flask, 715 mg (2.74 mmol) of 12 was dissolved in 10 mL CH₃COOH and 5 mL of H₂O. To this mixture was added 50 mg of 10% Pd on carbon, and the suspension was heated and stirred at reflux for 12 h. The mixture was cooled, filtered, and the solvents evaporated under reduced pressure. To the residue was added 20 mL of conc. NaHCO₃, and this mixture was extracted thoroughly with EtOAc. The pooled organic extracts were washed once with brine, dried over MgSO₄, and the solvents removed under reduced pressure to yield 605 mg of an orange oil that was pure (2R,5S)-1-(3-methoxyphenyl)-2,5-dimethylpiperazinium acetate by NMR. ¹H NMR (CDCl₃) δ 7.21 (t, 1H), 6.73 (dd, 1H), 6.62 (m, 1H), 6.67 (m, 1H), 6.63 (m, 1H), 3.79 (s, 3H), 3.12-2.90 (m, 4H), 2.70 (dd, 1H), 2.46 (dd, 1H), 1.07 (d, 3H), 0.93 (d, 3H). ESIMS: m/z 221 (M+H⁺, 100). General procedure c. was employed using 363 mg (1.65 mmol) of this oil affording a residue that was dissolved in 5 mL of MeOH and stirred over excess NaHCO₃. The mixture was filtered, and the solvents subjected to rotary evaporation to afford a residue that was purified by chromatography affording 215 mg of 13 as a white solid (63% yield). Spectral information for this compound was found to be identical to 17.

3-(4-Phenylpropylpiperazin-1-yl)phenol (5a) Dihydrochloride

General procedure e. was employed with 250 mg (0.735 mmol) of 9a. The crude product was subjected to flash-column chromatography on silica gel eluting with CMA80-CH₂Cl₂ (1:1). The freebase thus recovered was converted to the dihydrochloride salt by dissolving in 2 mL of a 2 M HCl solution in EtOH and removing the solvents under reduced pressure. The solids were suspended in EtOAc and collected by filtration to yield 55 mg (20%) of 5a.2HCl as a tan powder: mp 194-201° C. (dec). ¹H NMR (CD₃OD) δ 7.33-7.21 (m, 5H), 7.09 (t, 1H), 6.52-6.38 (m, 3H), 3.81-3.76 (bd, 2H), 3.67-3.63 (bd, 2H), 3.29-3.18 (m, 4H), 3.09-3.00 (bt, 2H), 2.75 (t, 2H), 2.13 (m, 2H). ESIMS: m/z 297 (M+H⁺, 100). Anal. calcd for C₁₉H₂₆Cl₂N₂O: C, 61.79; H, 7.10; N, 7.55. Found: C, 61.72; H, 7.10; N, 7.38.

(S)-3-(2-Methyl-4-phenylpropylpiperazin-1-yl)phenol (5b) Dihydrochloride

General procedure e. was employed using 247 mg (0.886 mmol) of 9b. The dihydrochloride salt was made by dissolving the crude product in 5 mL of a 2 M solution of HCl in EtOH and removing the solvents under reduced pressure. This salt was recrystallized from EtOH-EtOAc to yield 126 mg (37%) of 5b.2HCl as a white powder: mp>220° C. [α]=+2.17 (c 0.46, CH₃OH). The spectral information gathered for this compound were identical as those obtained for 5c (see below). Anal. calcd for C₂₀H₂₈Cl₂N₂O: C, 62.66; H, 7.36; N, 7.31. Found: C, 62.45; H, 7.53; N, 7.29.

(R)-3-(2-Methyl-4-phenylpropylpiperazin-1-yl)phenol (5c) Dihydrochloride

General procedure e. was employed using 175 mg (0.886 mmol) of 9c. The dihydrochloride salt was made by dissolving the product in 5 mL of a 2 M solution of HCl in EtOH and removing the solvents under reduced pressure. This salt was recrystallized from EtOH-EtOAc to yield 55 mg (19%) of 5c.HCl as a white powder: mp>220° C.; [α]−2.17 (c 0.46, CH₃OH). ¹H NMR (CD₃OD) δ 7.40-7.27 (m, 9H), 3.95-3.70 (b, 2H), 3.70-3.50 (b, 2H), 3.33 (m, 2H), 3.30 (m, 3H), 2.78 (t, 2H), 1.17 (d, 3H). ESIMS: m/z 311 (M+H⁺, 100). Anal. calcd for C₂₀H₂₈Cl₂N₂O: C, 62.66; H, 7.36; N, 7.31. Found: C, 62.15; H, 7.36; N, 7.02.

(Z)-3-(2,6-Dimethyl-4-(3-phenylpropyl)piperazin-1-yl)phenol (5d) Dihydrochloride

General procedure e. was employed using 65 mg (0.315 mmol) of 9d. The crude product was subjected to preparative TLC eluting with CMA80-CH₂Cl₂ (1:1) which afforded 20 mg (20%) of 5d as an amber-colored residue. The 5d.2HCl was prepared by dissolving this material in 5 mL of 2 M HCl in EtOH and removing the solvents under reduced pressure: mp 210-212° C. ¹H NMR (freebase in CDCl₃) δ 7.30-7.18 (m, 4H), 7.13 (t, 1H), 6.67 (d, 1H), 6.66 (s, 1H), 6.59 (dd, 1H), 3.19 (m, 2H), 2.81 (dd, 2H), 2.66 (t, 2H, J=9 Hz), 2.41 (dd, 2H), 2.08 (dd, 2H, J=9 Hz), 1.88 (m, 3H), 0.81 (d, 6H, J=6 Hz). ESIMS: m/z 325 (M+H⁺, 100). Anal. calcd for C₂₁H₃₀Cl₂N₂O.H₂O: C, 60.72; H, 7.76; N, 6.74. Found: C, 61.10; H, 7.80; N, 6.63.

3-[(2S,5S)-2,5-Dimethyl-4-(3-phenylpropyl)piperazin-1-yl]phenol (5e) Dihydrochloride

General procedure e. was employed using 83 mg (0.225 mmol) of 9e. The crude product was subjected flash column chromatography on silica gel eluting with CMA80-CH₂Cl₂ (1:1) which afforded an amber-colored residue. The dihydrochloride was prepared by dissolving this residue in 5 mL of 2 M HCl in EtOH and removing the solvents under reduced pressure. The residue was dissolved in 1 mL of MeOH, and the white crystals of 5e.2HCl were collected by filtration to afford 8 mg (9%): mp>220° C. (dec). ¹H NMR (freebase in CDCl₃) δ 7.30-7.18 (m, 4H), 7.13 (t, 1H), 6.67 (d, 1H), 6.66 (s, 1H), 6.59 (dd, 1H), 3.19 (m, 2H), 2.81 (dd, 2H), 2.66 (t, 2H, J=9 Hz), 2.41 (dd, 2H), 2.08 (dd, 2H, J=9 Hz), 1.88 (m, 3H), 0.81 (d, 6H, J=6 Hz). ESIMS: m/z 325 (M+H⁺, 100). Anal. calcd for C₂₁H₃₀Cl₂N₂O: C, 60.72; H, 7.76; N, 6.74. Found: C, 61.01; H, 7.70; N, 6.80.

(S)-3-(2,4-Dimethylpiperazin-1-yl)phenol (50 Dihydrochloride

At room temperature and under an atmosphere of H₂ were stirred 109 mg (0.567 mmol) of the piperazine 9b, 0.5 mL of Raney nickel slurry, and formaldehyde (0.5 mL of 37% in H₂O) in EtOH for 8 h in 15 mL of EtOH. The suspension was filtered and the solvents evaporated to yield a crude residue that was separated by silica gel column chromatography eluting with CMA80-CH₂Cl₂ (1:1). The fractions containing the product were removed of solvent by rotary evaporation, acidified with a 2 M HCl solution in EtOH, and crystallized by addition of Et₂O and cooling to give 5f.2HCl: mp 179-183° C.; [α]_(D)+4.4° (c 0.18, MeOH). ¹H NMR (freebase in CDCl₃) δ 7.09 (t, 1H), 6.50 (dd, 1H), 6.41 (t, 1H), 6.34 (dd, 1H), 3.75 (m, 1H), 3.15 (m, 1H), 2.76 (m, 1H), 2.55 (m, 2H), 2.36 (m, 1H), 2.32 (s, 3H), 1.06 (d, 3H). ESIMS: m/z 207 (M+1, 100). Anal. calcd for C₁₂H₂₀Cl₂N₂O: C, 51.62; H, 7.22; N, 10.03. Found: C, 51.88; H, 7.51; N, 9.89.

3-((2S,5R)-2,5-Dimethyl-4-(3-phenylpropyl)piperazin-1-yl)phenol (5g) Dihydrochloride

General procedure e. was employed using 175 mg (0.475 mmol) of 17. The dihydrochloride salt was made by dissolving the crude product in 5 mL of a 2 M solution of HCl in EtOH, and removing the solvents under reduced pressure. The salt was triturated under EtOH-iPrOH, collected by filtration, and dried under vacuum to afford 88 mg (47%) of pure 5g.HCl as a white powder: mp 199° C. (dec); [α]²⁵ _(D)−9.47 (c 0.57, MeOH). ¹H NMR (CD₃OD) δ 7.35-7.22 (m, 6H), 7.00-6.75 (m, 3H), 4.00-3.78 (m, 3H), 3.65-3.29 (m, 4H), 3.20 (dt, 1H), 2.80 (m, 2H), 2.15 (m, 1H), 1.38 (d, 3H), 1.11 (d, 3H). ESIMS: m/z 325 (M+H⁺, 100). Anal. calcd for C₂₁H₃₀Cl₂N₂O: C, 63.47; H, 7.61; N, 7.05. Found: C, 63.47; H, 7.67; N, 6.89.

3-((2R,5S)-2,5-Dimethyl-4-(3-phenylpropyl)piperazin-1-yl)phenol (5h) Dihydrochloride

General procedure e. was employed using 47 mg (0.228 mmol) of 13. The dihydrochloride salt was made by dissolving the crude product in 5 mL of a 2 M solution of HCl in EtOH, and removing the solvents under reduced pressure. The crude salt was triturated under EtOH-iPrOH, collected by filtration and dried under vacuum to afford 14 mg (15%) of pure 5h.2HCl as a white powder with identical melting point (199° C. dec) and spectra as those reported for 5g.2HCl: [α]²⁵ _(D)+9.5 (c 0.55, MeOH). Anal. calcd for C₂₁H₃₀Cl₂N₂O: C, 63.47; H, 7.61; N, 7.05. Found: C, 63.31; H, 7.51; N, 7.29.

3-{(2S)-4-[(2S)-2-Amino-3-methylbutyl]-2-methylpiperazin-1-yl}phenol (5i) Trihydrochloride

In a round-bottom flask, 570 mg (2.49 mmol) of 9b were dissolved in dry THF (30 mL) along with 542 mg (2.49 mmol) of N-Boc-L-valine. The solution was cooled to 0° C. in an ice-bath and 1.38 mL (9.97 mmol) of Et₃N were added followed by 1.10 g (2.49 mmol) of BOP. The flask was removed from the ice bath and the reaction was stirred for 2 h. The solution was then dumped on concentrated aqueous NaHCO₃ solution, and the mixture extracted three times with 15 mL of EtOAc. The pooled organic extracts were washed with brine, dried (MgSO₄), filtered, and the solution concentrated to leave a residue that was purified by flash column chromatography on silica gel to yield 415 mg (42%) of the intermediate amide. This amide was dissolved in 20 mL of THF, and 3.18 mL (3.18 mmol) of a 1 M solution of BH₃ THF were added. The solution was stirred at reflux overnight cooled to RT and quenched with 5 mL of H₂O. Into this solution was added 10 mL of conc. HCl, and the mixture was stirred for 1 hr and 20 mL of water were added. Solid NaHCO₃ was then added to adjust the solution to a pH of 8. The mixture was extracted three times with 5 mL of CH₂Cl₂, washed with brine, and dried (MgSO₄). Rotary evaporation of the solution afforded a residue that was purified by flash-column chromatography on silica gel eluting with CMA80-hexanes-EtOAc (6:2:1) to yield 241 mg (82%) of 5i as a white solid. An analytic sample of the trihydrochloride salt 5i.3HCl was prepared by recrystallization from EtOAc-hexanes: mp 210-212° C.; [α]²⁵ _(D)+48.8° (c 0.1, MeOH). NMR (CD₃OD) δ 7.46-7.40 (t, 1H), 7.16 (m, 2H), 6.98 (d, 1H), 4.14 (m, 1H), 3.96 (m, 1H), 3.65 (m, 1H), 3.30 (m, 3H), 2.95 (m, 3H), 2.00 (m, 1H) 1.23-1.03 (m, 9H). ESIMS: m/z 278 (M+H⁺, 100). Anal. calcd for C₁₆H₃₀Cl₃N₃O.H₂O: C, 47.47; C, 7.97; N, 10.38. Found: C, 47.02; H, 7.96; N, 10.03.

(3R)-7-Hydroxy-N-[(1S)-1-{[(3S)-4-(3-hydroxyphenyl)-3-methylpiperazin-1-yl]methyl}-2-methylpropyl]-1,2,3,4-tetrahydroisoquinoline-3-carboxamide (5j) Trihydrochloride

In a round-bottom flask, 120 mg (0.432 mmol) of 5i and 133 mg (0.454 mmol) of 7-OH-Boc-D-Tic were dissolved in dry THF (15 mL), and the solution was cooled to 0° C. Into this solution 0.06 mL of Et₃N were added followed by 201 mg (0.454 mmol) of BOP. The solution was warmed up to room temperature, stirred for 3 h, and then added to an ice-cold concentrated NaHCO₃ solution. The mixture was extracted three times with 5 mL of EtOAc. The pooled organic extracts were washed once with conc. NaHCO₃ solution, once with brine, and dried (MgSO₄). The filtrates were concentrated under reduced pressure to yield a residue that was dissolved in 5 mL of CH₂Cl₂ and 3 mL of CF₃CO₂H and stirred overnight. The solvents were reduced under reduced pressure to yield a residue, which was stirred with 10 mL of conc. NaHCO₃ solution and 10 mL of EtOAc. The layers were separated, and the aqueous layer was extracted three times with 3 mL of EtOAc. The pooled organic extracts were washed once with brine, dried (MgSO₄), and filtered. The filtrates were concentrated under reduced pressure to yield a residue that was purified by flash-column chromatography on silica gel eluting with CMA80-EtOAc-hexanes (2:1:1) to yield a residue that was dissolved in 3 mL of a 2 M solution of HCl in EtOH. The solvent was removed under reduced pressure to leave a solid that was triturated under MeOH to give 61 mg (31%) of 5j.3HCl: mp>220° C. (dec); [α]+67.6 (c 0.21, CH₃OH). ¹H NMR (CD₃OD) δ 8.75 (d, 1H), 7.38 (b, 1H), 7.10 (b+d, 3H), 6.92 (b, 1H), 6.76 (dd, 1H), 6.67 (d, 1H), 4.44-4.33 (m, 6H), 3.91-3.67 (m, 3H), 3.67-3.50 (m, 2H), 3.50-3.35 (m, 2H), 3.31-3.21 (m, 1H), 2.81 (dd, 1H) 1.92 (m, 1H), 1.18 (b, 3H), 1.05 (t, 6H). ESIMS: m/z 453 (M+H⁺, 100). Anal. calcd for C₂₆H₃₉Cl₃N₄O₃.3H₂O: C, 50.69; H, 7.36; N, 9.09. Found: C, 50.66; H, 7.09; H, 8.95.

TABLE 1 Comparison of Inhibition of Agonist Stimulated [³⁵S]GTPγS Binding in Cloned Human μ, δ, and κ-Opioid Receptors for Compounds

μ, DAMGO δ, DPDPE κ, U69,593 compd Structure R₁ R₂ R₃ R₄ R₅ K_(e) (nM) K_(e) (nM) K_(e) (nM) μ/κ δ/κ norBNI 26 ± 7  29 ± 8  0.05 ± 0.02 520  580 JDTic A ^(a) 25.1 ± 3.5  76.4 ± 2.7  0.02 ± 0.01 1255 3830 2b A CH₃ 29 ± 3  680 ± 240 155 ± 24  2c A C₆H₅(CH₂)₃ 0.10 ± 0.02 0.90 ± 0.3  0.88 ± 0.20 5a B H H H H C₆H₅(CH₂)₃ 8.5 ± 1.4 34 ± 6  15 ± 3  5b B H (S)CH₃ H H C₆H₅(CH₂)₃ 0.88 ± 0.03 13.4 ± 4.2  4.09 ± 0.79 5c B H (R)CH₃ H H C₆H₅(CH₂)₃ 1.0 ± 0.2 7.0 ± 2  1.5 ± 0.4 5d B (Z)CH₃, CH₃ H H C₆H₅(CH₂)₃ 3 4300  3 5e B H (S)CH₃ H (S)CH₃ C₆H₅(CH₂)₃ —  7 ± 0.3 5f B H (S)CH₃ H H CH₃ 508 ± 26  NA 193 ± 19  5g B H (S)CH₃ H (R)CH₃ C₆H₅(CH₂)₃ 6.1 ± 1.7 55 ± 3  4.2 ± 0.8 5h B H (R)CH₃ H (S)CH₃ C₆H₅(CH₂)₃ 18 ± 4  179 ± 68  26 ± 7  5i B H (S)CH₃ H H CH₂CH[(CH₃)₂CH]NH₂ 2  55 10 5j B H (S)CH₃ H H a 22 ± 4  274 ± 48  2.7 ± 0.1

Additional Examples A. Compound 12 and Intermediates

(2R,5R)-1-tert-butoxycarbonyl-2,5-dimethylpiperazine (19)

A solution of 1.43 g (5.19 mmol) of (2R,5R)-2,5-dimethyl piperazine dihydrobromide 18¹ was dissolved in 30 mL of MeOH along with 262 mg (2.59 mmol) of Et₃N. Into this solution was added 565 mg (2.59 mmol) of Boc₂O and the solution was stirred overnight. The solution was subjected to rotary evaporation and added 20 mL of CH₂Cl₂ and 20 ml of conc. NaHCO₃. The mixture was shaken thoroughly and the layers separated. The organic layer was extracted twice with conc. NaHCO₃ and the organic layer dried over MgSO₄, filtered and the solvents removed. The residue was purified by silica-gel column chromatography eluting with 2:1 CMA80:CH₂Cl₂ to yield 497 mg (84%) of pure 19 as a clear oil. ¹H NMR (CDCl₃): δ 4.28-4.02 (bd, 1H); 3.90-3.63 (bdd, 1H); 2.99-2.94 (dd, 1H); 2.81-2.75 (d, 1H); 2.71-2.62 (m, 1H); 2.53-2.49 (d, 6H); 1.25 (d, 3H); 1.06 (d, 3H). ESIMS: m/z 215 (M+H⁺, 100).

(2R,5R)-1-tert-butoxycarbonyl-4-(3-methoxyphenyl)-2,5-dimethylpiperazine (20)

General procedure b. was employed using 546 mg (2.55 mmol) of Boc-piperazine 19g to obtain, after chromatography, 515 mg (63%) of 20 as a yellow oil. ¹H NMR (CDCl₃): δ 7.17 (t, 1H, J=9 Hz); 6.52 (d, 1H); 6.47-6.45 (m, 1H); 4.15 (q, 1H, J=6 Hz); 4.03-3.98 (m, 1H); 3.41 (m, 1H); 3.30 (dd, 1H, J_(a)=6 Hz, J_(b)=12 Hz); 2.97-2.90 (dd, 1H, J_(a)=6 Hz J_(b)=12 Hz); 2.84 (dd, 1H J_(a)=12 Hz, J_(b)=3 Hz); 1.45 (s, 9H); 1.32 (d, 3H, J=6 Hz); 1.04 (d, 3H, J=6 Hz). ESIMS: m/z 321 (M+H⁺, 50).

(2R,5R)-3-(2,5-dimethylpiperazin-1-yl)phenol (21)

General procedure d. was employed using 515 mg (1.61 mmol) of 20 and 10 mL of conc. HBr. The dihydrobromide salt was dissolved in MeOH, stirred over 200 mg of NaHCO₃ for 10 minutes and then filtered. The solution was concentrated under reduced pressure and the crystallized from MeOH/Et₂O to yield 407 mg (69%) of 21e as a white solid: mp>220° C. ¹H NMR (CDCl₃): δ 7.10 (q, 1H); 6.52 (m, 1H); 6.45 (s, 1H); 6.41 (m, 1H); 4.23 (m, 2H); 3.89-3.39 (m, 4H); 3.03 (dd, 2H); 1.45 (d, 3H, J=6 Hz); 1.15 (d, 3H, J=6 Hz). ESIMS: m/z 207 (M+H⁺, 100).

3-[(2R,5R)-2,5-Dimethyl-4-(3-phenylpropyl)piperazin-1-yl]phenol dihydrochloride (22)

General procedure f. was employed using 300 mg (0.225 mmol) of 21. The dihydrochloride was prepared by addition of a 2 M HCl solution in EtOH and rotary evaporation. The crude HCl salt was recrystallized from EtOH/Et₂O to afford 260 mg (80%) of 22 as a white crystalline solid. MP>220° C. (dec). ¹H NMR (CD₃OD): δ 7.26-7.19 (m, 4H); 7.07 (m, 1H); 6.62 (m, 1H); 6.45 (d, 1H, J=9 Hz); 6.37-6.33 (m, 2H); 4.26 (m, 1H); 3.58-3.30 (m, 4H); 3.22-3.03 (m, 2H); 2.75 (t, 2H, J=5 Hz); 2.20-2.01 (m, 2H); 1.50 (d, 1H, J=6 Hz); 1.42 (d, 2H, J=6 Hz); 1.14 (d, 2H, J=6 Hz); 0.97 (d, 1H, J=6 Hz). ESIMS: m/z 325 (M+H⁺, 100). [α]_(D) ²⁵−12.3° (c 1, MeOH).

B. Process for the Preparation of Alkylpiperazines

2-Ethyl-piperazine (25)

The cyclic glycine-(2-ethyl-glycine) dipeptide 23^(2, 3) (0.11 g, 7.81 mmol) was suspended in 20 mL of dry THF and 31.2 mL of a 1 M solution of BH₃ THF were added. This mixture was stirred at reflux overnight cooled, and quenched with 10 mL of MeOH. Into this solution, 5 mL of conc. HBr were added, and the solvents were removed by rotary evaporation. The residue was recrystallized from MeOH/Et₂O giving 1.08 g of the product as a white solid. The freebase was made by dissolving the salt in MeOH, stirring over NaHCO₃, adding EtO₂, filtering and removing the solvents to yield a clear oil, ¹H NMR (CD₃OD): δ 30.91 (t, J=7 Hz, 3H), 1.20-1.30 (m, 2H), 2.30-3.30 (m, 7H). ESIMS: m/z 115 (M+H⁺, 100).

1-tert-butoxycarbonyl-3-ethyl-piperazine (26)

A solution of 1.00 g (3.62 mmol) of 2-ethylpiperazine dihydrobromide 25 in 10 mL of MeOH. was cooled to 0° C. Into this flask was added 0.50 mL (3.62 mmol) of Et₃N followed by a solution of 790 mg of Boc₂O in 10 mL added dropwise over 4 h. The mixture was stirred for 12 h and then subjected to rotary evaporation. The remaining residue was purified by silica-gel column chromatography eluting with 1:1 CMA80:CH₂Cl₂ affording 700 mg of 26 as a yellow oil. ¹H NMR (CDCl₃): δ 3.95 (bs, 2H); 2.97 (d, 1H, J=9 Hz); 2.77 (m, 2H); 2.48 (m, 2H); 1.46 (s, 9H); 1.40 (m, 2H); 0.95 (t, 3H, J=6 Hz) ESIMS: m/z 215 (M+H⁺, 75); 115 (M-Boc+H⁺, 100).

1-tert-butoxycarbonyl-3-ethyl-4-(3-methoxyphenyl)piperazine (27)

General procedure b. was employed using 0.30 g (5.35 mmol) of 26 to obtain, after chromatography, 0.20 g (44%) of 27 as a clear oil. ¹H NMR (CDCl₃): δ 7.17 (t, 1H, J=9 Hz); 6.47 (dd, 1H, J_(a)=3 Hz, J_(b)=9 Hz); 6.38 (s, 1H); 4.05 (s, 2H); 3.79 (s, 3H); 3.55 (m, 1H); 3.24-3.06 (m, 4H); 1.48 (m, 11H); 0.92 (t, 3H, J=9 Hz). ESIMS: m/z 321 (M+H⁺, 100).

3-(2-ethylpiperazin-1-yl)phenol dihydrobromide (28)

General procedure c. was employed using 200 mg (2.54 mmol) of 10c. The crude dihydrobromide was dissolved in 1 mL of MeOH stirred over NaHCO₃ and purified by silica-gel column chromatography eluting with 2:1 CMA80:CH₂Cl₂ to afford 105 mg of product was a clear oil. ¹H NMR (CD₃OD): δ 7.08 (t, 1H, J=9 Hz); 6.43 (d, 1H); 6.34 (s, 1H); 6.27 (d, 1H, J=9 Hz); 3.47 (m, 1H); 3.18 (m, 1H); 3.07-2.90 (m, 5H); 1.65 (m, 1H); 1.47 (m, 1H); 0.86 (t, 3H, J=6 Hz). ESIMS: m/z 207 (M+H⁺, 100).

3-[2-ethyl-4-(3-phenylpropyl)piperazin-1-yl]phenol dihydrochloride (29)

General procedure f. was employed using 100 mg (0.485 mmol) 10× to obtain, after salt formation, 55 mg of the dihydrochloride: mp 161-166° C. ¹H NMR (CD₃OD): δ 7.35-7.15 (m, 7H); 7.12 (bs, 1H); 6.91 (bs, 1H); 4.11-3.50 (m, 5H); 2.77 (t, 2H, J=6 Hz), 2.20 (m, 2H); 1.63 (m, 2H), 0.90 (t, 3H, J=6 Hz). ESIMS: m/z 325 (M+H⁺, 100).

C. Process for the synthesis of N-alkylamino 1-(3-hydroxyophenyl)-2-(S)-methylpiperazines Synthesis of N-substituted (S)-3-(2-methylpiperazin-1-yl)phenols 30 and 31

Compounds bearing 4-N-substituents were synthesized in a manner similar to compounds in the trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidines reported by Thomas et al⁴. (S)-3-(2-methylpiperazin-1-yl)phenol dihydrobromide was acylated using a series of amino acids and the peptide linking reagent HBTU. Without purification, the resulting amides were reduced with BH₃ THF to yield the N-substituted compounds 14.

General Procedure: Reductive Alkylation Using N-Boc-Protected Amino Acids

(S)-3-(2-methylpiperazin-1-yl)phenol dihydrobromide (100 mg, 0.282 mmol) and the N-Boc-protected amino acid (0.311 mmol) were dissolved in 1.5 mL of CH₃CN and 0.12 mL (0.847 mmol) of Et₃N. Into this mixture was added all at once, a solution of HBTU (118 mg, 0.311 mmol) in 2 mL of CH₃CN. The reaction was stirred overnight. To the reaction mixture were added 0.5 mL of CH₂Cl₂ followed by 2 mL of a saturated aqueous solution of NaHCO₃. The mixture was shake, and the organic layer separated and washed again with 2 mL conc. NaHCO₃. The solvents were dried over Na₂SO₄, filtered and the solution was rotary evaporated and placed under vacuum to yield a brown foam. This material was dissolved in 2 mL of dry THF and 2 mL of a 1 M solution of BH₃ THF and the solution stirred for 24 h. Carefully, 0.5 mL of conc. HCl were added and the mixture was stirred for 4 h, and subjected to rotary evaporation. The residue was purified by crystallization or silica-gel column chromatography.

3-{(2S)-4-[(2-amino-ethyl]-2-methylpiperazin-1-yl}phenol (31a)

The general procedure was employed using Boc-Glycine (54 mg, 0.311 mmol). The residue was crystallized from MeOH/Et₂O to yield 25 mg of the product as a tan solid: mp>230° C. ¹H NMR (CD₃OD): δ 7.40 (t, 1H, J=6 Hz); 7.10 (m, 2H); 6.93 (bd, 1H); 4.15 (m, 1H); 3.98-3.88 (bt, 1H); 3.75-3.68 (m, 1H); 3.60-3.50 (bd, 1H); 3.50-3.39 (bd, 1H); 3.15-3.01 (m, 2H); 1.36 (d, 3H, J=6 Hz). ESIMS: m/z 236 (M+H⁺, 100).

3-{(2S)-4-[(2R)-2-amino-propyl]-2-methylpiperazin-1-yl}phenol (31b)

The general procedure was employed using Boc-D-Alanine (59 mg, 0.311 mmol). The residue was crystallized from MeOH/Et₂O to yield 55 mg of the product as a white solid: mp 210-215° C. ¹H NMR (CD₃OD): δ 7.44 (t, 1H, J=6 Hz); 7.16 (m, 2H); 6.98 (m, 1H); 4.16 (bm, 1H); 3.99 (bt, 1H); 3.67 (m, 1H); 3.50-3.30 (m, 2H); 3.12-2.85 (bm, 3H); 1.36 (d, 3H, J=6 Hz); 1.17 (d, 3H, J=6 Hz). ESIMS: m/z 250 (M+H⁺, 100).

-   1. Tanatani, A.; Mio, M. J.; Moore, J. S., Chain Length-Dependent     Affinity of Helical Foldamers for a Rodlike Guest. Journal of the     American Chemical Society 2001, 123, (8), 1792-1793. -   2. Ognyanov, V. I.; Balan, C.; Bannon, A. W.; Bo, Y.; Dominguez, C.;     Fotsch, C.; Gore, V. K.; Klionsky, L.; Ma, V. V.; Qian, Y.-X.;     Tamir, R.; Wang, X.; Xi, N.; Xu, S.; Zhu, D.; Gavva, N. R.;     Treanor, J. J. S.; Norman, M. H., Design of Potent, Orally Available     Antagonists of the Transient Receptor Potential Vanilloid 1.     Structureâ^′ Activity Relationships of     2-piperazin-1-yl-1H-benzimidazoles. Journal of Medicinal Chemistry     2006, 49, (12), 3719-3742. -   3. Smith, G. G.; Evans, R. C.; Baum, R., Neighboring residue     effects: evidence for intramolecular assistance to racemization or     epimerization of dipeptide residues. Journal of the American     Chemical Society 1986, 108, (23), 7327-7332. -   4. Thomas, J. B.; Fall, M. J.; Cooper, J. B.; Rothman, R. B.;     Mascarella, S. W.; Xu, H.; Partilla, J. S.; Dersch, C. M.;     McCullough, K. B.; Cantrell, B. E.; Zimmerman, D. M.; Carroll, F.     I., Identification of an Opioid Kappa Receptor Subtype-Selective     N-Substituent for     (+)-(3R,4R)-Dimethyl-4-(3-hydroxyphenyl)piperidine. Journal of     Medicinal Chemistry 1998, 41, (26), 5188-5197.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

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The invention claimed is:
 1. An opioid receptor antagonist represented by the formula (I):

wherein R is OH, OC₁₋₆ alkyl, C₂₋₈ alkyl, C₁₋₈ haloalkyl, C₂₋₈ alkenyl, C₂₋₈ alkynyl, aryl substituted by one or more groups Y₁, CH₂-aryl wherein the aryl group is substituted by one or more groups Y₁, OCOC₁₋₈ alkyl, COC₁₋₈ alkyl, CONH₂, NHCHO, NH₂, NHSO₂C₁₋₈ alkyl, or NHCO₂C₁₋₈ alkyl; Y₃ is hydrogen, Br, Cl, F, CF₃, NO₂, OR₈, CO₂R₉, C₁₋₆ alkyl, NR₁₀R₁₁, NHCOR₁₂, NHCO₂R₁₂, CONR₁₃R₁₄ or CH₂(CH₂)_(n)Y₂; R₁, R₂, R₃ and R₄ are each, independently, one of the following structures:

or R₁ and R₂, R₂ and R₃ and/or R₃ and R₄ are bonded together to form a cyclo alkyl group or a bridged heterocyclic ring, wherein at least one of R₁, R₂, R₃ and R₄ is other than hydrogen; each Y₁ is, independently, hydrogen, OH, Br, Cl, F, CN, CF₃, NO₂, N₃, OR₈, CO₂R₉, C₁₋₆ alkyl, NR₁₀R₁₁, NHCOR₁₂, NHCO₂R₁₂, CONR₁₃R₁₄, or CH₂(CH₂)_(n)Y₂, or two adjacent Y₁ groups form a —O—CH₂—O— or —O—CH₂CH₂—O— group; each Y₂ is, independently, hydrogen, CF₃, CO₂R₉, C₁₋₈ alkyl, NR₁₀R₁₁, NHCOR₁₂, NHCO₂R₁₂, CONR₁₃R₁₄, CH₂OH, CH₂OR₈, COCH₂R₉,

each n is, independently, 0, 1, 2 or 3; each o is, independently, 0, 1, 2 or 3; each R₈, R₉, R₁₀, R₁₁, R₁₂, R₁₃ and R₁₄ is, independently, hydrogen, C₁₋₈ alkyl, CH₂-aryl wherein the aryl group is substituted by one or more substituents OH, Br, Cl, F, CN, CF₃, NO₂, N₃, C₁₋₆ alkyl, or CH₂(CH₂)_(n)Y₂′; each Y₂′ is, independently, hydrogen, CF₃, or C₁₋₆ alkyl; R₅ is

—CH₂CH₂—X—R₆, or

R₆ is C₂₋₈ alkenyl, C₁₋₄ alkyl substituted C₄₋₈ cycloalkyl, C₁₋₄ alkyl substituted C₄₋₈ cycloalkenyl, or thiophene; X is a single bond, —C(O)— or —CH(OR₁₅)—; R₁₅ hydrogen, C₁₋₆ alkyl, —(CH₂)_(q)-phenyl or —C(O)—R₁₆; R₁₆ is C₁₋₄ alkyl or —(CH₂)_(q)-phenyl; each q is, independently, 1, 2 or 3; R₁₇ is hydrogen, C₁₋₈ alkyl, CO₂C₁₋₈ alkylaryl substituted by one or more groups Y₁, CH₂-aryl substituted by one or more groups Y₁, or CO₂C₁₋₈ alkyl; R₁₈ is hydrogen, C₁₋₈ alkyl, C₂₋₈ alkenyl, C₃₋₈ alkynyl, CH₂CO₂C₁₋₈ alkyl, CO₂C₁₋₈ alkyl or CH₂-aryl substituted by one or more groups Y₁; R₁₉ is a group selected from the group consisting of structures (a)-(p):

Q is NR₂₁, CH₂, O, S, SO, or SO₂; each Y₄ is, independently, Br, Cl, F, CN, CF₃, NO₂, N₃, OR₂₂, CO₂R₂₃, C₁₋₆ alkyl, NR₂₄R₂₅, NHCOR₂₆, NHCO₂R₂₇, CONR₂₈R₂₉, or CH₂(CH₂)_(n)Y₂, or two adjacent Y₄ groups form a —O—CH₂—O— or —O—CH₂CH₂—O— group; p is 0, 1, 2, or 3; R₂₀ is hydrogen, C₁₋₈ alkyl, C₂₋₈ alkenyl, C₂₋₈ alkenyl, CH₂OR₃₀, or CH₂-aryl substituted by one or more substituents Y₁; each R₂₁ is, independently, hydrogen, C₁₋₈ alkyl, CH₂-aryl substituted by one or more substituents Y₁, NR₃₁R₃₂, NHCOR₃₃, NHCO₂R₃₄, CONR₃₅R₃₆, CH₂(CH₂)_(n)Y₂, or C(═NH)NR₃₇R₃₈; R₃₀ is hydrogen C₁₋₈ alkyl, C₂₋₈ alkenyl, C₂₋₈ alkenyl, CH₂O₂C₁₋₈ alkyl, CO₂C₁₋₈ alkyl, or CH₂-aryl substituted by one or more substituents Y₁; R₂₂, R₂₃, R₂₄, R₂₅, R₂₆, R₂₇, R₂₈, R₂₉, R₃₁, R₃₂, R₃₃, R₃₄, R₃₅, R₃₆, R₃₇ and R₃₈ are, independently, hydrogen, C₁₋₈ alkyl, CH₂-aryl substituted by one or more substituents OH, Br, Cl, F, CN, CF₃, NO₂, N₃, C₁₋₆ alkyl, or CH₂(CH₂)_(n)Y₂′; Z is N or S, wherein when Z is S, there is no R₁₈; X₁ is hydrogen, C₁₋₈ alkyl, C₂₋₈ alkenyl, or C₂₋₈ alkynyl; X₂ is hydrogen, C₁₋₈ alkyl, C₂₋₈ alkenyl, or C₂₋₈ alkynyl; or X₁ and X₂ together form ═O, ═S, or ═NH; or a pharmaceutically acceptable salt thereof.
 2. The opioid receptor antagonist of claim 1, wherein R is OH, OC₁₋₃ alkyl, C₁₋₄ alkyl, C₁₋₄ haloalkyl, C₂₋₄ alkenyl, C₂₋₄ alkynyl, aryl substituted by one or more groups Y₁, CH₂-aryl wherein the aryl group is substituted by one or more groups Y₁, OCOC₁₋₄ alkyl, COC₁₋₄ alkyl, CONH₂, NHCHO, NH₂, NHSO₂C₁₋₄ alkyl, or NHCO₂C₁₋₄ alkyl; and Y₃ is hydrogen, Br, Cl, F, CF₃, NO₂, OR₈, CO₂R₉, C₁₋₃ alkyl, NR₁₀R₁₁, NHCOR₁₂, NHCO₂R₁₂, CONR₁₃R₁₄ or CH₂(CH₂)_(n)Y₂.
 3. The opioid receptor antagonist of claim 2, wherein R₁, R₂, R₃ and R₄ are each, independently, one of the following structures:

or R₁ and R₂, R₂ and R₃ and/or R₃ and R₄ are bonded together to 5 to 7 membered alkyl group or a bridged heterocyclic ring, wherein at least one of R₁, R₂, R₃ and R₄ is other than hydrogen.
 4. The opioid receptor antagonist of claim 1, wherein R is OH, OC₁₋₂ alkyl, C₁₋₂ alkyl, C₁₋₂ haloalkyl, C₂₋₃ alkenyl, C₂₋₃ alkynyl, aryl substituted by one or more groups Y₁, CH₂-aryl wherein the aryl group is substituted by one or more groups Y₁, COC₁₋₂ alkyl, CONH₂, NHCHO, NH₂, NHSO₂C₁₋₂ alkyl, or NHCO₂C₁₋₂ alkyl.
 5. The opioid receptor antagonist of claim 1, wherein R is OH, OCH₃, OCF₃, COCH₃, OCOCH₃, CONH₂, NHCHO, NH₂, NHSO₂CH₃, or NHCO₂CH₃.
 6. The opioid receptor antagonist of claim 1, wherein R is OH, OCH₃, or OCF₃.
 7. The opioid receptor antagonist of claim 1, wherein Y₃ is hydrogen.
 8. The opioid receptor antagonist of claim 1, wherein R₁, R₂, R₃ and R₄ are each, independently, one of the following structures:

or R₁ and R₂, R₂ and R₃ and/or R₃ and R₄ are bonded together to 5 to 7 membered alkyl group or a bridged heterocyclic ring, wherein at least one of R₁, R₂, R₃ and R₄ is other than hydrogen.
 9. The opioid receptor antagonist of claim 1, wherein R₁, R₂, R₃ and R₄ are each, independently, hydrogen, methyl or ethyl, wherein at least one of R₁, R₂, R₃ and R₄ is other than hydrogen.
 10. The opioid receptor antagonist of claim 1, wherein R₁, R₂, R₃ and R₄ are each, independently, hydrogen or methyl, wherein at least one of R₁, R₂, R₃ and R₄ is methyl.
 11. The opioid receptor antagonist of claim 1, wherein R₁, R₂, R₃ and R₄ are each, independently, hydrogen or methyl, wherein at least one of R₁, R₂, R₃ and R₄ is methyl.
 12. The opioid receptor antagonist of claim 1, wherein R is OH, OCH₃, or OCF₃; Y₃ is hydrogen; and R₁, R₂, R₃ and R₄ are each, independently, hydrogen, methyl or ethyl, wherein at least one of R₁, R₇, R₁ and R₄ is other than hydrogen; and R₅ is —(CH₂)_(n)-phenyl, wherein n is
 3. 13. The opioid receptor antagonist of claim 1, wherein R₂ is other than hydrogen as defined above.
 14. The opioid receptor antagonist of claim 13, wherein R₂ is C₁₋₈ alkyl.
 15. The opioid receptor antagonist of claim 13, wherein R₂ is methyl or ethyl.
 16. The opioid receptor antagonist of claim 13, wherein R₂ is methyl.
 17. The opioid receptor antagonist of claim 1, wherein R₅ is

wherein n is 0, 1, 2 or
 3. 18. The opioid receptor antagonist of claim 1, wherein R₅ is

wherein n is 2 or
 3. 19. The opioid receptor antagonist of claim 1, wherein R₅ is

wherein n is 1, 2 or
 3. 20. The opioid receptor antagonist of claim 13, wherein R₅ is

wherein n is 0, 1, 2 or
 3. 21. The opioid receptor antagonist of claim 1, wherein R₅ is —CH₂CH₂—X—R₆.
 22. The opioid receptor antagonist of claim 1, wherein R₅ is


23. A pharmaceutical composition, comprising the opioid receptor antagonist of claim 1 and a pharmaceutically acceptable carrier. 